Hi Nguyen Gia Huy,
Thanks for your patience.
We have checked your provided excel file in that you are using merge cell functionality. We would like to inform you that we have included the merge cell support in our volume 1 release in version (18.1.42). So, we suggest you upgrade our Syncfusion packages to our latest version to resolve this issue in your end. We have created the sample for your convenience in this version (18.1.42) and your provided excel file is properly loaded in the below sample.
Sample Link:
Regards,
Arunkumar D